Integral composite membrane with a continuous ionomer phase

ABSTRACT

Embodiments are directed to composite membranes having a microporous polymer structure, and an ion exchange material forming a continuous ionomer phase within the composite membrane. The continuous ionomer phase refers to absence of any internal interfaces in a layer of ionomer or between any number of layers coatings of the ion exchange material provided on top of one another. The composite membrane exhibits a haze change of 0% or less after being subjected to a blister test procedure. No bubbles or blisters are formed on the composite membrane after the blister test procedure. A haze value of the composite membrane is between 5% and 95%, between 10% and 90% or between 20% and 85%. The composite membrane may have a thickness of more than 17 microns at 0% relative humidity.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.17/262,516, filed Jan. 22, 2021, which is a national phase applicationof PCT Application No. PCT/US2018/044104, internationally filed on Jul.27, 2018, which are herein incorporated by reference in their entiretiesfor all purposes.

FIELD OF THE INVENTION

The present invention relates to an integral composite membrane, and inparticular, to a composite membrane having a continuous ionomer phase.

BACKGROUND OF THE INVENTION

Composite membranes such as anion, cation, and amphoteric compositemembranes are used in a variety of applications. For example, compositemembranes are components of polymer electrolyte fuel cells where thecomposite membranes are located between a cathode and anode, andtransport protons formed near a catalyst at a hydrogen electrode to anoxygen electrode thereby allowing a current to be drawn from the polymerelectrolyte fuel cells. These polymer electrolyte fuel cells areparticularly advantageous because they operate at lower temperaturesthan other fuel cells. Also, these polymer electrolyte fuel cells do notcontain any corrosive acids which are found in phosphoric acid fuelcells.

A composite membrane may also be used for electrochemical devices toseparate liquids contained within the electrochemical device such aselectrolysis cell or flow battery, such as redox flow battery. The flowbattery is charged and discharged by a reversible reduction-oxidationreaction between the two liquid electrolytes of the battery. Ionexchange (i.e., providing flow of electric current) occurs through thecomposite membrane while the two liquid electrolytes circulate in theirown respective space within the flow battery. The flow battery is ascalable system which can be operated in a wide range of conditions. Forexample, the flow battery can be integrated into smart-grids, and isadvantageous in connection with storing energy from wind or solar farms.The flow battery is further characterized by high longevity in the rangeof several years, easy maintenance, and overall energy efficiency.

Composite membranes incorporated into fuel cells as well as thoseemployed in, redox flow battery, chlor-alkali electrolysis cells, waterelectrolysis, diffusion dialysis, electrodialysis, pervaporation, andvapor permeation applications typically comprise ionomer films having adiscontinuous ionomer phase constructed from multiple coatings of anionomer. However, these ionomer film composite membranes can suffer frompremature structural failure in a flow battery application. The primarymode of failure for these ionomer film composite membranes duringoperation of the flow battery is the formation of bubbles or blistersinside of the membrane in a layer of ionomer or between the multiplecoatings of the ionomer. Accordingly, the need exists for improvedcomposite membranes that have a continuous ionomer phase, high ionconductance, low crossover of reactive species, high mechanicalstrength, and low in-plane swelling.

SUMMARY OF THE INVENTION

In one embodiment, the invention relates to a composite membrane foraredox flow battery. The composite membrane includes a microporouspolymer structure, and an ion exchange material at least partiallyembedded within the microporous polymer structure and rendering at leasta portion of the microporous polymer structure occlusive. The ionexchange material forms a continuous ionomer phase within the compositemembrane. The composite membrane exhibits a haze change of 0% or lessafter being subjected to a blister test procedure. The blister testprocedure may include at step one immersing the composite membrane for 3minutes in an 6 mol/L aqueous sulfuric acid solution at 80° C.; at steptwo, removing the composite membrane from the aqueous sulfuric acidsolution; at step three, immersing the composite membrane for one minutein deionized water at ambient conditions; at step four removing thecomposite membrane from the deionized water; repeating cycle composed ofsteps one through four consecutively for at least two times; at stepfive, drying the composite membrane at ambient conditions; and at stepsix, counting bubbles or blisters formed on the composite membrane.According to various embodiments, no bubbles or blisters are formed onthe composite membrane after the blister test procedure (i.e. zerobubbles or blisters are counted on the composite membrane). In someembodiments, a haze value of the composite membrane is between 5% and95%, between 10% and 90% or between 20% and 85%.

In some embodiments, the composite membrane includes a single coating ofthe ion exchange material. The composite membrane may have a thicknessof 7 to 100 microns at 0% relative humidity, 17 to 50 microns at 0%relative humidity or 25 to 40 microns at 0% relative humidity. Thecomposite membrane according to various embodiments may have a thicknessof more than 17 microns at 0% relative humidity.

In some embodiments, the composite membrane includes multiple coatingsof the ion exchange material. In such embodiments, a first coating ofthe ion exchange material is formed on a second coating of the ionexchange material without subjecting the second coating to a dryingstep. The composite membrane may have a thickness of to 150 microns at0% relative humidity, 15 to 80 microns at 0% relative humidity, or to 60microns at 0% relative humidity.

According to various embodiments, the ion exchange material may haveequivalent weight between 500 and 2000 g/mole eq., between 700 and 1500g/mole eq., or between 900 and 1200 g/mole eq, or between 810 and 1100g/mole eq.

According to various embodiments, the composite membrane furthercomprises an additional layer of ion exchange material provided at abottom surface of the composite membrane. In some embodiments, themicroporous polymer structure comprises at least two microporous polymerlayers. In some embodiments, the composite membrane comprises more thanone ion exchange material in the form of a mixture of ion exchangematerials. Yet in other embodiments, the composite membrane comprisesmore than one layer of ion exchange material, such that the layers ofion exchange material are formed of the same ion exchange material ordifferent ion exchange materials.

In another embodiment, the invention relates to a composite membrane fora redox flow battery. The composite membrane includes a microporouspolymer structure and ion exchange material at least partially embeddedwithin the microporous polymer structure and rendering at least aportion of the microporous polymer structure occlusive. The ion exchangematerial forms a continuous ionomer phase within the composite membrane.The composite membrane has a thickness of more than 17 microns at 0%relative humidity. For example, the composite membrane may have athickness of 7 to 100 microns at 0% relative humidity, 17 to 50 micronsat 0% relative humidity or 25 to 40 microns at 0% relative humidity.

In another embodiment, the invention relates to a composite membrane fora redox flow battery. The composite membrane includes a microporouspolymer structure and ion exchange material at least partially embeddedwithin the microporous polymer structure and rendering at least aportion of the microporous polymer structure occlusive. The ion exchangematerial forms a continuous ionomer phase within the composite membrane.The composite membrane has a thickness of more than 17 microns at 0%relative humidity. For example, the composite membrane may have athickness of 7 to 100 microns at 0% relative humidity, 17 to 50 micronsat 0% relative humidity or 25 to 40 microns at 0% relative humidity. Thecomposite membrane exhibits a haze change of 0% or less after beingsubjected to a blister test procedure. That is, a haze value of thecomposite membrane remains the same or reduces from before to afterbeing subjected to the blister test procedure. According to variousembodiments, a haze value of the composite membrane is between 5% and95%, between 10% and 90% or between 20% and 85%.

In another embodiment, a method of forming the above described compositemembrane(s) is provided. The method comprises providing a support layer,and applying an ion exchange material to the support layer in one step.The method further includes obtaining a microporous polymer structurecomprising at least one microporous polymer layer. The method furtherincludes laminating the at least one microporous polymer layer to theion exchange material to form an impregnated microporous polymerstructure having a continuous ionomer phase. The impregnated microporouspolymer structure is then dried and thermally annealed to form thecomposite membrane.

In other embodiments, a flow battery comprising the above describedcomposite mem brane(s) is provided. The flow battery may include acathode reservoir including a positive electrolyte fluid, an anodereservoir including a negative electrolyte fluid, and an exchange regionincluding the above-described composite membrane positioned betweenfirst side having a positive electrode and second side having a negativeelectrode. The cathode reservoir is connected via a first pump to thefirst side of the exchange region, and the anode reservoir is connectedvia a second pump to the second side of the exchange region.

In other embodiments, a composite membrane is provided, where thecomposite membrane is prepared by a process comprising obtaining anuntreated microporous polymer structure, applying an impregnant solutioncomprising an ion exchange material to the untreated microporous polymerstructure to form a treated microporous polymer structure having acontinuous ionomer phase; and drying and thermally annealing the treatedmicroporous polymer structure to form the composite membrane, whereinthe ion exchange material forms a continuous ionomer phase within thecomposite membrane, wherein the composite membrane exhibits a hazechange of 0% or less after being subjected to a blister test procedure.

Other aspects and variants of the invention will become evident in theensuing discussion.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be better understood in view of the followingnon-limiting figures, in which:

FIGS. 1A-1C show photomicrographs of a cross-section of a compositemembrane comprising bubbles or blisters;

FIGS. 2A and 2B show photomicrographs of a cross-section of a compositemembrane having a discontinuous ionomer phase comprising bubbles orblisters within an interface between two ionomers;

FIG. 3A shows a cross sectional side view of a composite membrane inaccordance with some aspects of the invention;

FIGS. 3B-3D show exemplary flow diagrams of processes for constructingexemplary composite membranes in accordance with some aspects of theinvention;

FIGS. 3E-3F show photomicrographs of a composite membrane with poroussubstrate characterized by nodes interconnected by fibrils and acontinuous ionomer phase, according to various embodiments;

FIG. 4 shows schematic of a flow battery comprising a composite membranein accordance with some aspects of the invention;

FIGS. 5A-5B show a schematic of a haze test arrangement for measuringtotal light transmittance of a composite membrane in accordance withsome aspects of the invention;

FIGS. 6A-6B show an exemplary composite membrane prepared in accordancewith aspects of the present invention and a conventional ion exchangemembrane, respectively, before and after the blister test; and

FIGS. 7A-7C show samples of composite membrane prepared in accordancewith aspects of the present invention after the blistering test inaccordance with some aspects of the invention.

DETAILED DESCRIPTION OF THE INVENTION I. Introduction

In one embodiment, the present invention is directed to a compositemembrane comprising a porous substrate with an impregnant comprising anion exchange material (e.g., an ionomer film composite membrane). Oneproblem associated with traditional ionomer film composite membranes,however, is their reduced ability to maintain structural integrity,particularly when employed in flow batteries. For example, it has beendiscovered that bubbles or blisters may form in the ionomer filmcomposite membranes inside of the membrane at weak internal interfacesin a layer of ionomer or between multiple coatings of the ionomer thatoriginate from traditional multiple pass coating processes employed forthe production of the ionomer film composite membranes. FIGS. 1A-1C showphotomicrographs of traditional ionomer film composite membranes 100having bubbles or blisters 110 in weak internal interfaces 120 betweenmultiple coatings 130 of the ionomer.

A traditional multiple pass coating process for creating an ionomer filmcomposite membrane comprises a first pass ionomer coating, whichincludes contacting a porous substrate such as expandedpolytetrafluoroethylene (ePTFE) with an impregnant such asperfluorosulfonic acid polymers to form a first pass ionomer. The firstpass ionomer is then heated in an oven to dry and thermally anneal theporous substrate with the impregnant. Subsequently, a second passionomer coating is applied to the already dried first pass ionomer,contacted with a porous substrate to create a second pass ionomer, andthe second pass ionomer is dried. Optionally, additional pass ionomercoatings can be applied on top of one another, contacted with poroussubstrates, and dried and annealed. The resulting structure ischaracterized by a discontinuous ionomer phase having an internalinterface between each of the ionomers, e.g., between the first passionomer and the second pass ionomer. FIGS. 2A-2B show photomicrographsof traditional ionomer film composite membranes 200 having adiscontinuous ionomer phase 210 with bubbles or blisters 220 formed atan internal interface 230 between each of the ionomers 240. Fibril-likestructures 250 are observed within the bubbles or blisters 220.

Without being bound by theory, the liquid electrolytes used in a flowbattery may be attracted to the internal interface in a layer of ionomeror between each of the ionomers, which may lead to the presence of anosmotic pressure gradient inside of the composite membrane duringoperation of the flow battery. The osmotic pressure gradient acts as adriving force for drawing water into the internal interface duringoperation of the flow battery. A hydraulic expansive force associatedwith the water being drawn into the internal interface leads to theformation of the bubbles or blisters between each of the ionomers.

To address these problems, in one embodiment, the present invention isfurther directed to composite membranes having a continuous ionomerphase. As used herein, “continuous ionomer phase” means any number oflayers or coatings of porous substrate and/or ion exchange materialprovided on top of one another that do not have any internal interfacesin a layer of ionomer or between the layers or coatings. Integralinterfaces may be caused, for example, by drying and thermally annealingof the porous substrate and/or ion exchange material prior toapplication of a subsequent layer or coating. In some embodiments, asingle pass ionomer coating process is performed, as described herein,to create a single pass ionomer composite membrane having a continuousionomer phase. The composite membrane made with single pass ionomercoating optionally has a thickness in the range of 7 to 100 microns at0% relative humidity (RH), 17 to 50 microns at 0% RH, or 25 to 40microns at 0% RH and optionally comprises between 3 g/m² and 80 g/m² ofporous substrate, or 5 g/m² and 50 g/m² of porous substrate, or 10 g/m²and 30 g/m² of porous substrate. In alternative embodiments, a multiplepass ionomer coating process is performed without a drying step betweeneach pass of coating, as described herein, to create a multiple passionomer composite membrane having a continuous ionomer phase. Themultiple pass ionomer composite membrane optionally has a thickness inthe range of 10 to 150 microns at 0% RH, 15 to 80 microns at 0% RH, or20 to 60 microns at 0% RH and optionally comprises between 3 g/m² and 80g/m² of porous substrate, or 5 g/m² and 50 g/m² of porous substrate, or10 g/m² and 30 g/m² of porous substrate. In some embodiments, an ionexchange material of specific equivalent weight is used for ionomercoating process, as described herein, to create a composite membranehaving a continuous ionomer phase. The ion exchange material optionallyhas equivalent weight between 500 and 2000 g/mole eq., or between 700and 1500 g/mole eq., or between 700 and 1200 g/mole eq, or between 810and 1100 g/mole eq. In some embodiments, a single or multiple passionomer coating process is performed without a drying step between eachpass of coating, as described herein, to create a composite membranehaving a continuous ionomer phase with pre-determined haze. The haze ofcomposite membrane optionally is between 5% and 95%, or 10% and 90%, or20% and 85%. The composite membrane optionally exhibits a reduction orno change in its haze value after such membrane is subjected to theblister test procedure. Accordingly, the present invention, in oneembodiment, is directed to composite membranes having a continuousionomer phase that does not have internal interfaces in a layer ofionomer or between multiple coatings of the ionomer, and exhibitsdesirable high ion conductance, low crossover of reactive species, highmechanical strength, and low in-plane swelling characteristics.

Various definitions used in the present disclosure are provided below.

As used herein, the terms “ionomer” and “ion exchange material” refer toa cation exchange material, an anion exchange material, or an ionexchange material containing both cation and anion exchangecapabilities. Mixtures of ion exchange materials may also be employed.Ion exchange material may be perfluorinated or hydrocarbon-based.Suitable ion exchange materials include, for example, perfluorosulfonicacid polymers, perfluorocarboxylic acid polymers, perfluorophosphonicacid polymers, styrenic ion exchange polymers, fluorostyrenic ionexchange polymers, polyarylether ketone ion exchange polymers,polysulfone ion exchange polymers, bis(fluoroalkylsulfonyl)imides,(fluoroalkylsulfonyl)(fluorosulfonyl)imides, polyvinyl alcohol,polyethylene oxides, divinyl benzene, metal salts with or without apolymer, and mixtures thereof. In exemplary embodiments, the ionexchange material comprises perfluorosulfonic acid (PFSA) polymers madeby copolymerization of tetrafluoroethylene and perfluorosulfonyl vinylester with conversion into proton form. Of course, the suitability of aparticular ion exchange material depends to a certain extent on theapplication for which the composite membrane is intended. Examples ofsuitable perfluorosulfonic acid polymers for use in fuel cell or flowbattery applications include Nafion® (E.I. DuPont de Nemours, Inc.,Wilmington, Del., US), Flemion® (Asahi Glass Co. Ltd., Tokyo, JP), andAciplex® (Asahi Chemical Co. Ltd., Tokyo, JP), which are commerciallyavailable perfluorosulfonic acid copolymers. Other examples of suitableperfluorosulfonic acid polymers for use in fuel cell applicationsinclude perfluorinated sulfonyl (co)polymers such as those described inU.S. Pat. No. 5,463,005.

As used herein “continuous ionomer phase” refers to an ionomer with nointernal interface. A continuous ionomer phase may refer, but is notlimited, to a composite membrane made with single pass ionomer coating.A composite membrane made with single pass ionomer coating may containone or more layers of material that are formed on top of each other(e.g. coating of a imbibed layer (e.g. an ionomer layer impregnated inthe microporous polymer structure) formed on a backer layer, laminatedwith a microporous polymer layer) and dried and thermally annealed (e.g.cured)).

As used herein, the term “microporous polymer structure” refers to apolymeric matrix that supports the ion exchange material, addingstructural integrity and durability to the resulting composite membrane.In exemplary embodiments, the microporous polymer structure comprisesexpanded polytetrafluoroethylene having a node and fibril structure. Themicroporous structure described herein has pores that are not visible tothe naked eye. According to various optional embodiments, the pores mayhave an average pore size from 0.01 to 100 microns, e.g., from 0.05 to10 microns or from 0.1 to 1 microns.

In some embodiments the microporous polymer structure is expandedpolytetrafluoroethylene having an average pore size from 0.01 to 100microns, e.g., from 0.05 to 10 microns or from 0.1 to 1 microns.

As used herein, an interior volume of a microporous polymer structure isreferred to as “substantially occluded” when said interior volume hasstructures that is characterized by low volume of voids, less than 10%by volume, and being highly impermeable to gases, Gurley numbers largerthan 10000 s. Conversely, interior volume of microporous polymerstructure is referred to as “non-occluded” when said interior volume hasstructures that is characterized by large volume of voids, more than 10%by volume, and being permeable to gases, Gurley numbers less than 10000s.

In some embodiments the microporous polymer structure is expandedpolytetrafluoroethylene having an average pore size from 0.01 to 100microns, e.g., from 0.05 to 10 microns or from 0.1 to 1 microns, andvoids less than 10% by volume.

A suitable microporous polymer structure depends largely on theapplication in which the composite membrane is to be used. Themicroporous polymer structure preferably has good mechanical properties,is chemically and thermally stable in the environment in which thecomposite membrane is to be used, and is tolerant of any additives usedwith the ion exchange material for impregnation. A suitable microporouspolymer structure for redox flow battery or fuel cell applications mayinclude porous polymeric materials. The porous polymeric materials mayinclude fluoropolymers, chlorinated polymers, hydrocarbons, polyamides,polycarbonates, polyacrylates, polysulfones, copolyether esters,polyvinylidene fluoride, polyaryl ether ketones, polybenzimidazoles,poly(ethylene-co-tetrafluoroethylene),poly(tetrafluoroethylene-co-hexafluoropropylene). In some embodiments,the microporous polymer structure includes a perfluorinated porouspolymeric material. The perfluorinated porous polymeric material mayinclude polytetrafluoroethylene (PTFE), expanded polytetrafluoroethylene(ePTFE), polyvinylidene fluoride (PVDF), expanded polyvinylidenefluoride (ePVDF), expanded poly(ethylene-co-tetrafluoroethylene)(eEPTFE) or mixtures thereof. In some embodiments, the microporouspolymer structure includes a hydrocarbon material. The hydrocarbonmaterial may include polyethylene, expanded polyethylene, polypropylene,expanded polypropylene, polystyrene, or mixtures thereof. Examples ofsuitable perfluorinated porous polymeric materials for use in redox flowbattery or fuel cell applications include ePTFE made in accordance withthe teachings of U.S. Pat. No. 8,757,395, which is incorporated hereinby reference in its entirety, and commercially available in a variety offorms from W. L. Gore & Associates, Inc., of Elkton, MD.

II. Composite Membranes

Composite membranes, having either a continuous ionomer phase or adiscontinuous ionomer phase, have a predetermined haze. Haze refers tothe wide-angle scattering of light by the composite membrane resultingin loss of optical contrast with which an object can be seen when viewedthrough the composite membrane. Haze can be measured with a haze meteror transparency meter as described herein in detail. The compositemembranes with continuous ionomer phase do not blister. Accordingly, thehaze of composite membranes with continuous ionomer phase does notchange after the blister test or continuous operation in flow battery.On the other hand, composite membranes with discontinuous ionomer phase(i.e. composite membranes without continuous ionomer phase) do blister.Accordingly, the haze of composite membranes with discontinuous ionomerphase changes after the blister test or continuous operation in flowbattery. The haze in composite membranes with continuous ionomer phaseis similar to the haze in composite membranes without continuous ionomerphase before the blister test. However, the haze in composite membraneswith continuous ionomer phase is different from the haze in compositemembranes without continuous ionomer phase after the blister test.

Composite membranes, having either a continuous ionomer phase or adiscontinuous ionomer phase, also have a predetermined bubble or blisterdensity that can be measured after the membrane is used continuously ina flow battery for a predetermined amount of time or exposed to ablister test procedure as described in detail herein. The area of thebubbles or blisters is measured as a ratio of the area of the compositemembrane to the area of the bubbles or blisters in the compositemembrane.

In some embodiments, the predetermined bubble or blister density of acomposite membrane with continuous ionomer phase formed via a singlepass ionomer coating and after continuous use in a flow battery for 10days is less than 0.3%, less than 0.2%, or less than 0.1, or 0%. Inalternative embodiments, the bubble or blister area of a continuousionomer phase formed via multiple passes of ionomer coating without adrying step between each pass of coating and after continuous use in aflow battery for 10 days is less than 0.3%, less than 0.2%, or less than0.1% or 0%. In other embodiments, the bubble or blister area of acomposite membrane with continuous ionomer phase formed via a singlepass ionomer coating and after exposure to a blister test procedure isless than 0.3%, less than 0.2%, or less than 0.1%, or 0. In alternativeembodiments, the bubble or blister area of a continuous ionomer phaseformed via multiple passes of ionomer coating without a drying stepbetween each pass of coating and after exposure to a blister testprocedure is less than 0.3%, less than 0.2%, or less than 0.1%, or 0%.In some embodiments, the change in haze of a composite membrane withcontinuous ionomer phase formed via a single pass ionomer coating andafter exposure to the blister test procedure is 0% or less, between 0%and −60%, or between 0% and −45%, or between 0% and −30%, or between 0%and −21%. In alternative embodiments, the change in haze of a compositemembrane with continuous ionomer phase formed via multiple passes ofionomer coating without a drying step between each pass of coating andafter exposure to a blister test is 0% or less, between 0% and −60%, orbetween 0% and −45%, or between 0% and −30%, or between 0% and −21%.

a. Composite Membranes Having A Continuous Ionomer Phase

As discussed above, the composite membrane according to variousembodiments have a continuous ionomer phase. As shown in FIG. 3A, acomposite membrane 301 is provided that includes a microporous substrate306 and an impregnant comprising an ion exchange material or ionexchange resin 304 that is characterized by a continuous ionomer phase350 (i.e., absence of interfaces between ionomer coatings). The poroussubstrate 306 is a membrane defined by a thickness of less than 0.4 mm(400 microns). The ion exchange resin 304 substantially impregnates theporous substrate 306 so as to render the interior volume substantiallyocclusive. For example, by filling greater than 90% of the interiorvolume of the porous substrate 306 with the ion exchange resin 304substantial occlusion will occur.

The composite membrane of the present disclosure may be employed invarious applications. In some embodiments, the composite membrane of thepresent disclosure may be employed in polarity-based chemicalseparations, pervaporation, gas separation, dialysis separation,industrial electrochemistry such as chlor-alkali electrolysis and otherelectrochemical applications, use as a super acid catalyst, or use as amedium in enzyme immobilization. In preferred embodiments, the compositemembrane of the present disclosure may be used in electrochemicalapplications to separate liquids contained within an electrochemicaldevice. In a preferred embodiment, the composite membrane of the presentdisclosure may be employed in fuel cells. In another preferredembodiment, the composite membrane of the present disclosure may beemployed in water electrolysis cells, water electrolyzers. In yetanother preferred embodiment, the composite membrane of the presentdisclosure may be employed in flow batteries, such as redox flowbatteries.

The impregnant comprises the ion exchange material or ion exchange resin304. The ion exchange material or ion exchange resin 304 is a cationexchange material, an anion exchange material, or an ion exchangematerial containing both cation and anion exchange capabilities.Mixtures of ion exchange materials may also be employed as impregnates.

Optionally, the impregnant solution further includes a surfactant. Thesurfactant may be employed with the ion exchange material to ensureimpregnation of the interior volume of the porous substrate. Surfactantsor surface active agents having a hydrophobic portion and a hydrophilicportion may be utilized. Preferable surfactants are those having amolecular weight of greater than 100 and may be classified as anionic,nonionic, or amphoteric which may be hydrocarbon or fluorocarbon-basedand include for example, Merpol®, a hydrocarbon based surfactant orZonyl®, a fluorocarbon based surfactant, both commercially availablefrom E. I. DuPont de Nemours, Inc. of Wilmington, DE.

In various embodiments, the surfactant is a nonionic material,octylphenoxy polyethoxyethanol having a chemical structure:

where x=10 (average) known as Triton X-100, commercially available fromRohm & Haas of Philadelphia, Pa.

The impregnant may further comprise other components, if desired. Forexample, the impregnant may comprise an electrocatalyst composition.Suitable catalyst compositions include unsupported and supportedcatalysts comprising precious metals, transition metals, oxides thereof,alloys thereof, and mixtures thereof. The presence of electrocatalyst inthe ion exchange layer of the composite membrane may be desirable forreducing reactant crossover, such as, for example, methanol in directmethanol fuel cell applications. Further, the electrocatalyst mayprovide for more effective ionomer-electrocatalyst interactions, therebyfacilitating the oxidation and reduction of reactant gases.

The impregnant may further comprise electrochemically inert materialsthat promote water retention in the composite membrane under normaloperating conditions. Polymeric, non-polymeric or hydrogel materials maybe suitable. For example, the impregnant may further compriseparticulate silica and/or fibrous silica, as described in U.S. Pat. No.5,523,181, which is incorporated herein by reference, or a hydrogelcomprising silicon oxides, such as described in Chemistry of Materials,Vol. 7, pp. 2259-2268 (1995). Other suitable such materials will beapparent to persons skilled in the art.

The impregnant may further comprise compatible mixtures of non-ionicpolymers, such as polyarylether ketones or polysulfones, for example.Having non-ionic polymers in the impregnant may be advantageous in someapplications. For example, non-ionic polymers in the impregnant mayreduce the amount of methanol cross-over in direct methanol fuel cells.

In embodiments, in which a polymeric composition is used, the impregnantis typically introduced into the porous substrate via an impregnationsolution comprising the impregnant in a suitable solvent. The choice ofsolvent will depend, in part, on both the composition of the impregnantand the composition of the porous substrate. Suitable solvents include,for example, water, ethanol, propanol, butanol, methanol, ketones,carbonates, tetrahydrofuran, acetonitrile N,N-dimethylformamide,N-methylpyrrolidone, dimethylsulfoxide, N,N-dimethylacetamide, andmixtures thereof. As used herein, “solvent” means any suitable solventor mixture of solvents.

Alternatively, the ion exchange material may comprise one or moremonomers or oligomers that may be impregnated into the porous substrateand subsequently polymerized or otherwise chemically linked. Thus, asused herein, “impregnant solution” includes ion exchange monomers,oligomers, polymers, and/or mixtures thereof in solvent, as well as neation exchange material monomers and/or oligomers. Note that where theimpregnation solution comprises components in addition to the ionexchange material, such components need not be dissolved in the liquidphase. Thus, impregnation solutions may also be dispersions.

In one embodiment, a composite membrane fora redox flow battery mayinclude an expanded polytetrafluoroethylene having an average pore sizefrom 0.01 to 100 microns; and a perfluoro sulfonic acid resin with EW of810 to 1100 g/(mole acid equivalence) at least partially embedded withinthe microporous polymer structure and rendering at least a portion ofthe microporous polymer structure occlusive. The perfluoro sulfonic acidresin forms a continuous ionomer phase within the composite membrane.The composite membrane exhibits a haze change of 0% or less after beingsubjected to a blister test procedure.

b. Processes for Preparing the Composite Membranes

FIGS. 3B-3C show exemplary flow diagrams of processes 340 and 360 forconstructing exemplary composite membranes 300 and 380, respectively, inaccordance with various aspects of the disclosure. The flow diagramsillustrate the architecture, functionality, and operation of possibleimplementations of systems and methods according to various embodimentsof the present disclosure. In some alternative implementations, where itmakes logical sense to do so, the functions noted in each block mayoccur out of the order noted in the figure. For example, two blocksshown in succession may, in fact, be executed substantiallyconcurrently, or the blocks may sometimes be executed in the reverseorder, depending upon the functionality, process, or end productinvolved.

Referring to FIG. 3B, exemplary flow diagram of process 340 illustratesa method for forming a composite material 300 having a fully imbibedmicroporous polymer structure 307, an additional layer of ion exchangematerial 305 and an uncoated non-occlusive layer 309. The process 340incudes providing a support structure like a backer 302.

Suitable support structures may comprise woven materials which mayinclude, for example, scrims made of woven fibers of expanded porouspolytetrafluoroethylene; webs made of extruded or oriented polypropyleneor polypropylene netting, commercially available from Conwed, Inc. ofMinneapolis, Minn.; and woven materials of polypropylene and polyester,from Tetko Inc., of Briarcliff Manor, N.Y. Suitable non-woven materialsmay include, for example, a spun-bonded polypropylene from Reemay Inc.of Old Hickory, Tenn. In other aspects, the support structure caninclude web of polyethylene (“PE”), polystyrene (“PS”), cyclic olefincopolymer (“COC”), cyclic olefin polymer (“COP”), fluorinated ethylenepropylene (“FEP”), perfluoroalkoxy alkanes (“PFAs”), ethylenetetrafluoroethylene (“ETFE”), polyvinylidene fluoride (“PVDF”),polyetherimide (“PEI”), polysulfone (“PSU”), polyethersulfone (“PES”),polyphenylene oxide (“PPO”), polyphenyl ether (“PPE”), polymethylpentene(“PMP”), polyethyleneterephthalate (“PET”), or polycarbonate (“PC”). Insome aspects, the support structure also includes a protective layer,which can include polyethylene (PE), polystyrene (“PS”), cyclic olefincopolymer (“COC”), cyclic olefin polymer (“COP”), fluorinated ethylenepropylene (“FEP”), perfluoroalkoxy alkanes (“PFAs”), ethylenetetrafluoroethylene (“ETFE”), polyvinylidene fluoride (“PVDF”),polyetherimide (“PEI”), polysulfone (“PSU”), polyethersulfone (“PES”),polyphenylene oxide (“PPO”), polyphenyl ether (“PPE”), polymethylpentene(“PMP”), polyethyleneterephthalate (“PET”), or polycarbonate (“PC”).

In yet other aspects, support structure can include support structureoptionally may include a reflective layer that includes a metalsubstrate (e.g., an aluminum substrate). The specific metal chosen mayvary widely so long as it is reflective. A non-limiting list ofexemplary metals includes: aluminum, beryllium, cerium, chromium,copper, germanium, gold, hafnium, manganese, molybdenum, nickel,platinum, rhodium, silver, tantalum, titanium, tungsten, zinc, or alloyssuch as Inconel or bronze. The reflective layer optionally comprises amixture or alloy of two or more metals, optionally two or more of themetals listed above. The reflective layer optionally can include a highreflectivity polymeric multilayer film such as Vikuiti™ EnhancedSpecular Reflector available from 3M company. In yet another example,the reflective layer optionally can include a high reflectivitynon-metal inorganic dielectric multilayer film comprised of materialssuch as, for example, magnesium fluoride, calcium fluoride, titaniumdioxide, silicon dioxide.

At step 342, a first ion exchange material is applied as a layer ofcontrolled thickness to the support structure in a single or multiplepass ionomer coating technique including forward roll coating, reverseroll coating, gravure coating, doctor coating, kiss coating, slot diecoating, slide die coating, as well as dipping, brushing, painting, andspraying. The first ion exchange material may be prepared by dissolvingan ion exchange material in a solvent. The first ion exchange materialmay comprise ion exchange material and a solvent, and optionallyadditional components such as a surfactant. In some embodiments, the ionexchange material is a cation exchange material, an anion exchangematerial, or an ion exchange material containing both cation and anionexchange capabilities. The choice of solvent may depend, in part, onboth the composition of the ionomer and the composition of the poroussubstrate.

At step 344, an untreated microporous polymer structure is laminatedover at least a portion of the first ion exchange material by anyconventional technique, such as, for example, hot roll lamination,ultrasonic lamination, adhesive lamination, contact lamination or forcedhot air lamination so long as the technique does not damage theintegrity of the untreated microporous polymer structure. In someembodiments, the untreated microporous polymer structure comprises ePTFEhaving a microporous polymer structure. The microporous polymerstructure can be characterized by uniform structure and compositionthroughout its entire thickness. In other aspects, structure andcomposition of microporous polymer structure can vary throughout itsthickness. The prepared or obtained microporous polymer structure mayhave a thickness of less than 400 microns, for example from 1 microns to400 microns at 0% relative humidity. The mass per unit area of theuntreated microporous polymer structure may be greater than 0.05 g/m²,for example from 0.3 g/m² to 80 g/m² at 0% relative humidity.

For example, a carrier support like a backer can be continuously fedfrom a roller unwind station via alignment and tension rollers to acoating station. The ion exchange material can be applied as a layer ofcontrolled thickness onto the surface of the carrier support (backer) bysuitable coating means, such as, for example, a doctor blade. Theuntreated microporous polymer structure may be continuously fed from aroller unwind station to an alignment roller and contacts the coatedcarrier support and is impregnated with ion exchange material.Alternatively, the carrier support can be eliminated and the layer ofion exchange material can be directly applied to the untreatedmicroporous polymer structure.

At step 346, the treated microporous polymer structure is placed into anoven to dry and thermally anneal and finalize construction of acomposite membrane. The oven temperature may be greater than 60° C., forexample from 60° to 220° C. or from 150° to 200° C. Drying and thermallyannealing the treated microporous polymer structure in the oven causesthe ion exchange material to become securely adhered to the internalmembrane surfaces, and optionally the external membrane surfaces, e.g.,the fibrils and/or nodes of the microporous polymer structure. Theresulting dried and annealed composite membrane 300 may have a thicknessof larger than 17 microns, for example from 17 microns to 100 microns at0% relative humidity. The mass of the composite membrane may be greaterthan 30 g/m², for example from 30 g/m² to 200 g/m² at 0% relativehumidity.

Referring now to FIG. 3C, exemplary flow diagram of process 360illustrates a method for forming a composite material 380 having a fullyimbibed microporous polymer structure 307, an additional layer of ionexchange material 305 and a partially coated non-occlusive layer 319.The process 360 incudes providing a support structure (e.g. backer) 302,such as a woven material, similar to the process 340.

At step 362, a first ion exchange material is applied as a layer ofcontrolled thickness to the support structure (backer) similar to step342 of the process 340. The description of step 362 is omitted here asit is identical to step 342 of the process 340, described above.

At step 364, an untreated microporous polymer structure is laminatedover a first portion of the first ion exchange material by anyconventional technique, such as, hot roll lamination, ultrasoniclamination, adhesive lamination, contact lamination or forced hot airlamination so long as the technique does not damage the integrity of theuntreated microporous polymer structures. In some embodiments, theuntreated microporous polymer structure comprises ePTFE having amicroporous polymer structure. The microporous polymer structure can becharacterized by uniform structure and composition throughout its entirethickness. In other aspects, structure and composition of themicroporous polymer structure can vary throughout its thickness.

After the lamination, a touch roll 310 may be used to coat a top portionof the microporous polymer structure with, for example, ionomer coating.

Step 366 is similar to step 346 of the process 340. Accordingly, thedescription of step 366 is omitted here. The dried and annealed preparedor obtained microporous polymer structure may have a thickness of morethan 17 microns, for example from 17 microns to 100 microns at 0%relative humidity. The mass of the composite membrane may be greaterthan 30 g/m², for example from 30 g/m² to 200 g/m² at 0% relativehumidity.

Referring now to FIG. 3D, exemplary flow diagram of process 320illustrates a method for forming a composite material 321 having a fullyimbibed microporous polymer structure 307, and two additional layers ofion exchange material 305. The process 320 incudes providing a supportstructure (e.g. backer) 302, such as a woven material, similar to theprocesses 340 and 360.

At step 322, a first ion exchange material is applied as a layer ofcontrolled thickness to the support structure (backer) similar to step342 of the process 340. The description of step 322 is omitted here asit is identical to step 342 of the process 340, described above.

At step 324, an untreated microporous polymer structure is laminatedover a first portion of the first ion exchange material by anyconventional technique, such as, hot roll lamination, ultrasoniclamination, adhesive lamination, contact lamination or forced hot airlamination so long as the technique does not damage the integrity of theuntreated microporous polymer structures. In some embodiments, theuntreated microporous polymer structure comprises ePTFE having amicroporous polymer structure. The microporous polymer structure can becharacterized by uniform structure and composition throughout its entirethickness. In other aspects, structure and composition of themicroporous polymer structure can vary throughout its thickness.

After the lamination, at step 326, a second ion exchange material 327 isapplied as a layer of controlled thickness to the top side ofmicroporous polymer structure using ionomer coating technique includingforward roll coating, reverse roll coating, gravure coating, doctorcoating, kiss coating, slot die coating, slide die coating, as well asdipping, brushing, painting, and spraying. The second ion exchangematerial may be prepared by dissolving an ion exchange material in asolvent. The second ion exchange material may comprise ion exchangematerial and a solvent, and optionally additional components such as asurfactant. In some embodiments, the ion exchange material is a cationexchange material, an anion exchange material, or an ion exchangematerial containing both cation and anion exchange capabilities. Thechoice of solvent may depend, in part, on both the composition of theionomer and the composition of the porous substrate.

Step 328 is similar to step 346 of the process 340. Accordingly, thedescription of step 328 is omitted here. The dried and annealed preparedor obtained composite membrane may have a thickness of more than 17microns, for example from 17 microns to 100 microns at 0% relativehumidity. The mass of the composite membrane may be greater than 30g/m², for example from 30 g/m² to 200 g/m² at 0% relative humidity.

Processes 340, 360 and 320 may include optional steps of submerging thecomposite membrane and boiling the composite membrane. For example, inembodiments in which a surfactant is employed, the composite membrane isfurther processed to remove the surfactant. This is accomplished bysoaking or submerging the composite membrane in a solution of, forexample, water, isopropyl alcohol, hydrogen peroxide, methanol, and/orglycerin. During this step, the surfactant, which was originally mixedin solution with the ion exchange material, is removed. This soaking orsubmerging causes a slight swelling of the composite membrane, howeverthe ion exchange material remains within the interior volume of theporous substrate.

At optional step of boiling, the composite membrane is treated byboiling in a suitable swelling agent, preferably water, causing thecomposite membrane to slightly swell in the x, y, and z direction. Theswollen composite membrane has a higher and stronger ion transport rate.The swollen composite membrane retains its mechanical integrity anddimensional stability unlike membranes consisting only of the ionexchange material, and simultaneously maintains desired ionic transportcharacteristics. A correlation exists between the content of theswelling agent within composite membrane and transport properties of thecomposite membrane. A swollen composite membrane will transport chemicalspecies faster than an un-swollen composite membrane.

As shown in FIGS. 3B-3D, a composite membrane 300, 380, 321 includes amicroporous polymer structure 306 and an ion exchange material (e.g.ionomer) 304 impregnated in the microporous polymer structure 306. Thatis, the microporous polymer structure 306 is imbibed with the ionexchange material 304. The ion exchange material 304 may substantiallyimpregnate the microporous polymer structure 306 so as to render theinterior volume substantially occlusive (i.e. the interior volume havingstructures that is characterized by low volume of voids and being highlyimpermeable to gases). For example, by filling greater than 90% of theinterior volume of the microporous polymer structure 306 with the ionexchange material 304, substantial occlusion will occur and membranewill be characterized by Gurley numbers larger than 10000 s. The ionexchange material 304 is securely adhered to the internal and externalsurfaces of the microporous polymer structure 306, e.g., the fibrilsand/or nodes of the microporous polymer structure 306 forming an imbibedlayer 307.

In some embodiments, the ion exchange material 304, in addition to beingimpregnated in the microporous polymer structure 306 in the imbibedlayer 307, is provided as one or more additional layers 305 (e.g.,referred also as “butter coat (BC)”) on one or more external surfaces ofthe imbibed layer 307.

As illustrated in the composite membrane 300 shown in FIG. 3B, part ofthe microporous polymer structure 306 (e.g. top surface area or bottomsurface area) may include a non-occlusive (i.e. the interior volumehaving structures that is characterized by high volume of voids andbeing highly permeable to gases) layer 309 that is free or substantiallyfree of the ion exchange material 304. The location of the non-occlusivelayer 309 is not limited to the top surface area of the microporouspolymer structure 306. As provided above, the non-occlusive layer 309may be provided on a bottom surface area of the microporous polymerstructure 306.

As illustrated in the composite membrane 380 shown in FIG. 3C, thenon-occlusive layer 319 may include a small amount of the ion exchangematerial 304 present in an internal surface of the microporous polymerstructure 306 as a thin node and fibril coating. However, the amount ofthe ion exchange material 304 may be not be large enough to render themicroporous polymer structure 306 occlusive, thereby forming thenon-occlusive layer 319.

In some embodiments, the composite membrane 300, 380, 321 may beprovided on a support layer 302. The support layer 302 may include abacker, a release film such as, for example, cycloolefin copolymer (COC)layer. In some embodiments, the composite membrane 300, 380, 321 may bereleased (or otherwise uncoupled) from the support layer 302 prior tobeing incorporated in a membrane electrode assembly (MEA).

FIGS. 3B-3D illustrate exemplary composite membranes 300, 380, 321 thatinclude a single type of ion exchange material 304. However, theapplication is not limited to composite membranes having a single typeof ion exchange material 304 or a single imbibed layer 307.

FIGS. 3E-3F illustrate photomicrographs of a composite membrane withporous substrate characterized by nodes interconnected by fibrils and acontinuous ionomer phase, according to various embodiments. As shown inFIGS. 3E-3F, a composite membrane prepared in accordance with aspects ofthe present invention has a uniform thickness free of any internalinterfaces in a layer of ionomer or between multiple coatings of theionomer, and free of any discontinuities or pinholes on the surface. Theinterior volume of the composite membrane is substantially occluded suchthat the composite membrane is impermeable to non-polar gases and to thebulk flow of liquids.

c. Preparation and Application of the Impregnant Solution

Referring back to steps 342, 362 and 322, further details about thepreparation and application of an impregnant solution on the supportstructure is described next.

The impregnant solution is prepared by dissolving an ion exchangematerial in a solvent. The impregnant solution comprising the ionexchange material in the solvent, and optionally other components suchas a surfactant. The ion exchange material is a cation exchangematerial, an anion exchange material, or an ion exchange materialcontaining both cation and anion exchange capabilities. The choice ofsolvent will depend, in part, on both the composition of the impregnantand the composition of the porous substrate.

The impregnant solution may be applied as a layer of controlledthickness to the untreated porous substrate in a single pass ionomercoating technique including forward roll coating, reverse roll coating,gravure coating, doctor coating, kiss coating, as well as dipping,brushing, painting, and spraying so long as the liquid solution is ableto penetrate the interstices and interior volume of the untreated poroussubstrate. Excess solution from the surface of the treated poroussubstrate may be removed. For example, a carrier support can becontinuously fed from a roller unwind station via alignment and tensionrollers to a coating station. The impregnant solution can be applied asa layer of controlled thickness onto the surface of the carrier supportby suitable coating means, such as, for example, a doctor blade. Theuntreated porous substrate may be continuously fed from a roller unwindstation to an alignment roller and contacts the coated carrier supportand is impregnated with impregnant solution. Alternatively, the carriersupport can be eliminated and the layer of impregnant solution can bedirectly applied to the untreated porous substrate.

The resulting treated porous substrate or composite membrane made withsingle pass ionomer coating has a thickness in the range of 7 to 100microns, 17 to 50 microns, or 25 to 40 microns and optionally comprisesbetween 3 g/m² and 80 g/m² of porous substrate, or 5 g/m² and 50 g/m² ofporous substrate, or 10 g/m² and 30 g/m² of porous substrate. As shouldbe understood, the single pass ionomer coating results in a compositemembrane having a continuous ionomer phase that does not have internalinterfaces in a single coating of ionomer.

In some embodiments, the impregnant solution is applied as multipleadditional layers of controlled thickness (i.e., a multiple passionomer) to a surface of the treated porous substrate by a similarcoating technique, such as, for example, forward roll coating, reverseroll coating, gravure coating, doctor coating, kiss coating, as well asdipping, brushing, painting, and spraying. For example, the treatedporous substrate may be continuously fed to an alignment roller andcontacts the coated carrier support one or more additional times(multiple passes) and is impregnated with impregnant solution.Alternatively, the carrier support can be eliminated and the layer ofimpregnant solution can be directly applied multiple times to thetreated porous substrate. This process can be repeated any number oftimes (e.g., twice) without a drying step between each pass of coatingto create the treated porous substrate with multiple layers. Theresulting multiple pass composite membrane, has a thickness in the rangeof 10 to 150 microns at 0% RH, 15 to 80 microns at 0% RH, or 20 to 60microns at 0% RH and optionally comprises between 3 g/m² and 80 g/m² ofporous substrate, or 5 g/m² and 50 g/m² of porous substrate, or 10 g/m²and 30 g/m² of porous substrate. As should be understood, the multiplepass ionomer coating results in one or multiple layers of treated poroussubstrate having a continuous ionomer phase that does not have internalinterfaces in a layer of ionomer or between the multiple coatings of theionomer.

In alternative embodiments, another untreated porous substrate may bebrought into contact with the coated and treated porous substrate, andthe untreated porous substrate is impregnated with the impregnantsolution to create a treated porous substrate with multiple layers(i.e., a multiple pass ionomer composite membrane). This process can berepeated any number of times (e.g., twice) without a drying step betweeneach pass of coating to create the treated porous substrate withmultiple layers. The resulting multiple pass composite membrane, has athickness in the range of 10 to 150 microns at 0% RH, 15 to 80 micronsat 0% RH, or 20 to 60 microns at 0% RH and optionally comprises between3 g/m² and 80 g/m² of porous substrate, or 5 g/m² and 50 g/m² of poroussubstrate, or 10 g/m² and 30 g/m² of porous substrate. As should beunderstood, the multiple pass ionomer coating results in a compositemembrane with one or multiple layers of treated porous substrate havinga continuous ionomer phase that does not have internal interfaces in alayer of ionomer or between the multiple coatings of the ionomer.

The treated porous substrate may be placed into an oven to dry andthermally anneal. Oven temperatures may range from 60° to 220° C., butpreferably between 150° and 200° C. Drying and thermally annealing thetreated porous substrate in the oven causes the ion exchange material tobecome securely adhered to the internal membrane surfaces and optionallyto the external membrane surfaces, e.g., the fibrils and/or nodes of theporous substrate.

In embodiments in which a surfactant is employed, the treated poroussubstrate is further processed to remove the surfactant. This isaccomplished by soaking or submerging the treated porous substrate in asolution of, for example, water, isopropyl alcohol, hydrogen peroxide,methanol, and/or glycerin. During this step, the surfactant, which wasoriginally mixed in solution with the ion exchange material, is removed.This soaking or submerging causes a slight swelling of the treatedporous substrate, however the ion exchange material remains within theinterior volume of the porous substrate.

The treated porous substrate is treated by boiling in a suitableswelling agent, preferably water, causing the membrane to slightly swellin the x, y, and z direction. The swollen treated porous substrate has ahigher and stronger ion transport rate. The swollen treated poroussubstrate retains its mechanical integrity and dimensional stabilityunlike membranes consisting only of the ion exchange material, andsimultaneously maintains desired ionic transport characteristics. Acorrelation exists between the content of the swelling agent withintreated porous substrate and transport properties of the treated poroussubstrate. A swollen treated porous substrate will transport chemicalspecies faster than an un-swollen treated porous substrate.

d. Properties of the Composite Membrane

Composite membranes having a continuous ionomer phase in accordance withaspects of the present invention have a predetermined clarity. Hazerefers to the optical distinctness with which an object can be seen whenviewed through the composite membrane, and can be measured with a Hazemeter or transparency meter. In some embodiments, the haze of acomposite membrane with continuous ionomer phase formed via a singlepass ionomer coating is between 5% and 95%, or 10% and 90%, or 20% and85%. In alternative embodiments, the haze of a continuous ionomer phaseformed via multiple passes of ionomer coating without a drying stepbetween each pass of coating is between 5% and 95%, or 10% and 90%, or20% and 85%.

III. Flow Batter

As discussed above, the composite membrane manufactured in accordancewith aspects of the present invention (see, e.g., FIGS. 3A-3F) may beincorporated in a flow battery (e.g. a redox flow battery). As shown inFIG. 4 , a flow battery 400 is provided in accordance with aspects ofthe present invention. Flow battery 400 is a fully rechargeableelectrical energy storage device comprising a reservoir 410 including acatholyte or positive electrolyte fluid 420 and a second reservoir 430including an anolyte or negative electrolyte fluid 440. The catholyte420 may be an electrolyte containing specified redox ions which are inan oxidized state and are to be reduced during the discharge process offlow battery 400, or are in a reduced state and are to be oxidizedduring the charging process of the flow battery 400, or which are amixture of these oxidized ions and ions to be oxidized. The anolyte 440may be an electrolyte, containing redox ions which are in a reducedstate and are to be oxidized during a discharge process of the flowbattery 400, or are in an oxidized state and are to be reduced duringthe charging process of the flow battery 900, or which are a mixture ofreduced ions and ions to be reduced.

The catholyte 420 is circulated via pump 450 through an exchange region460 comprising a composite membrane 465 positioned between a positiveelectrode 470 and a negative electrode 480. The anolyte 440 iscirculated via pump 490 also through the exchange region 460. Thecomposite membrane 465 is manufactured in accordance with aspects of thepresent invention (see, e.g., FIGS. 3A-3D).

In some embodiments, the amount of the catholyte 420 and the anolyte 440provided to the exchange region 460 may be varied depending on a pumpingoperation of the pumps 450 and 490, and accordingly, the amount of powergenerated by reaction of electrolytes in the exchange region 460 may bevaried. Both the catholyte 420 and the anolyte 440 circulate in theirown respective space promoting reduction/oxidation chemical processes onboth sides of the composite membrane 465 resulting in an electricalpotential. Cell voltage may be chemically determined by the Nernstequation, and ranges from 0.5 to 5.0 volts or from 0.8 to 1.7 volts.

IV. Test Procedures

A. Tests for the Ion Exchange Material

(a) Solids Concentration of Solutions of the Ion Exchange Material (IEM)

Herein, the terms “solution” and “dispersion” are used interchangeablywhen referring to IEMs. This test procedure is appropriate for solutionsin which the IEM is in proton form, and in which there are negligiblequantities of other solids. A volume of 2 cubic centimeters of IEMsolution was drawn into a syringe and the mass of the syringe withsolution was measured via a balance in a solids analyzer (obtained fromCEM Corporation, USA). The mass of two pieces of glass fiber paper(obtained from CEM Corporation, USA) was also measured and recorded. TheIEM solution was then deposited from the syringe into the two layers ofglass fiber paper. The glass fiber paper with the ion exchange materialwas placed into the solids analyzer and heated up to 160° C. to removethe solvent liquids. Once the mass of the glass fiber paper and residualsolids stopped changing with respect to increasing temperature and time,it was recorded. It is assumed that the residual IEM contained no water(i.e., it is the ionomer mass corresponding to 0% RH). After that, themass of the emptied syringe was measured and recorded using the samebalance as before. The ionomer solids in solution was calculatedaccording to the following formula:

$\begin{Bmatrix}{{wt}\%{solids}{of}} \\{{IEM}{solution}}\end{Bmatrix} = {\frac{\begin{Bmatrix}{{Mass}{of}{glass}} \\{{fiber}{paper}{with}} \\{{residual}{solids}}\end{Bmatrix} - \begin{Bmatrix}{{Mass}{of}} \\{{glass}{fiber}} \\{paper}\end{Bmatrix}}{\begin{Bmatrix}{{Mass}{of}} \\{{full}{syringe}}\end{Bmatrix} - \begin{Bmatrix}{{Mass}{of}} \\{{emptied}{syringe}}\end{Bmatrix}} = \lbrack {{wt}\%} \rbrack}$

(b) Equivalent Weight of the Ion Exchange Material (IEM)

The following test procedure is appropriate for IEM comprised of asingle ionomer resin or a mixture of ionomer resins that is in theproton form (i.e., that contains negligible amounts of other cations),and that is in a solution that contains negligible other ionic species,including protic acids and dissociating salts. If these conditions arenot met, then prior to testing the solution must be purified from ionicimpurities according to a suitable procedure as would be known to one ofordinary skill in the art, or the impurities must be characterized andtheir influence on the result of the EW test must be corrected for.

As used herein, the EW of an IEM refers to the case when the IEM is inits proton form at 0% RH with negligible impurities. The IEM maycomprise a single ionomer or a mixture of ionomers in the proton form.An amount of IEM solution with solids concentration determined asdescribed above containing 0.2 grams of solids was poured into a plasticcup. The mass of the ion exchange material was measured via aconventional laboratory scale (obtained from Mettler Toledo, LLC, USA).Then, 5 ml of deionized water and 5 ml of 200 proof denatured ethanol(SDA 3C, Sigma Aldrich, USA) is added to ion exchange material in thecup. Then, 55 ml of 2N sodium chloride solution in water was added tothe IEM solution. The sample was then allowed to equilibrate underconstant stirring for 15 minutes. After the equilibration step, thesample was titrated with 1N sodium hydroxide solution. The volume of 1Nsodium hydroxide solution that was needed to neutralize the samplesolution to a pH value of 7 was recorded. The EW of the IEM (EW_(IEM))was calculated as:

${EW}_{IEM} = {\frac{\begin{Bmatrix}{{Mass}{of}} \\{{IEM}{solution}}\end{Bmatrix} \times \begin{Bmatrix}{{wt}\%{solids}{of}} \\{{IEM}{solution}}\end{Bmatrix}}{\begin{Bmatrix}{{Volume}{of}} \\{{NaOH}{solution}}\end{Bmatrix} \times \begin{Bmatrix}{{Normality}{of}} \\{{NaOH}{solution}}\end{Bmatrix}} = \lbrack \frac{g}{{mole}{{eq}.}} \rbrack}$

When multiple IEMs were combined to make a composite membrane, theaverage EW of the IEMs in the composite membrane was calculated usingthe following formula:

EW_(IEM_average)= $\lbrack {\frac{\begin{Bmatrix}{{Mass}{fraction}} \\{{of}{IEM}1}\end{Bmatrix}}{\{ {EW}_{{IEM},1} \}} + \frac{\begin{Bmatrix}{{Mass}{fraction}} \\{{of}{IEM}2}\end{Bmatrix}}{\{ {EW}_{{IEM},2} \}} + {\ldots.\frac{\begin{Bmatrix}{{Mass}{fraction}} \\{{of}{IEM}N}\end{Bmatrix}}{\{ {EW}_{{IEM},N} \}}}} \rbrack^{- 1} =$$\lbrack \frac{g}{{mole}{{eq}.}} \rbrack,$

where the mass fraction of each IEM is with respect to the total amountof all IEMs. This formula was used both for composite membranescontaining ionomer blends and for composite membranes containing ionomerlayers.

B. Tests for the Porous Membrane

(a) Bubble Point of the Porous Membrane

The Bubble Point was measured according to the procedures of ASTMF316-86 (1986). Isopropyl alcohol was used as the wetting fluid to fillthe pores of the test specimen. The Bubble Point is the pressure of airrequired to create the first continuous stream of bubbles detectable bytheir rise through the layer of isopropyl alcohol covering themicroporous polymer matrix. This measurement provides an estimation ofmaximum pore size.

(b) Gurley Number of the Porous Membrane

Gas flow barrier properties were measured using Gurley Densometeraccording to ASTM D-726-58 (1971). The procedure includes clampingsample between air permeable plates of the Gurley Densometer. An innercylinder of known weight that can slide freely is then released. TheGurley number is defined as time in seconds it takes for the releasedinner cylinder to displace a certain volume of air in the Densometerthrough the sample material.

(c) Non-Contact Thickness of the Porous Membrane

A sample of microporous polymer structure was placed over a flat smoothmetal anvil and tensioned to remove wrinkles. Height of microporouspolymer structure on anvil was measured and recorded using a non-contactKeyence LS-7010M digital micrometer. Next, height of the anvil withoutmicroporous polymer matrix was recorded. Thickness of the microporouspolymer structure was taken as a difference between micrometer readingswith and without microporous structure being present on the anvil.

(d) Mass-Per-Area of the Porous Membrane

Each Microporous Polymer structure was strained sufficient to eliminatewrinkles, and then a 10 cm² piece was cut out using a die. The 10 cm²piece was weighed on a conventional laboratory scale. The mass-per-area(M/A) was then calculated as the ratio of the measured mass to the knownarea. This procedure was repeated 2 times and the average value of theM/A was calculated.

(e) Apparent Density of the Porous Membrane

Apparent density of microporous polymer structure was calculated usingthe non-contact thickness and mass-per-area data using the followingformula:

${{Apparent}{density}_{{microporous}{layer}}} = {\frac{\{ {M/A_{{microporous}{layer}}} \}}{\{ {{non} - {contact}{thickness}} \}} = \lbrack {g/{cc}} \rbrack}$

C. Tests for the Composite Membrane

(a) Thickness of the Composite Membrane

The composite membranes were equilibrated in the room in which thethickness was measured for at least 1 hour prior to measurement.Composite membranes were left attached to the substrates on which thecomposite membranes were coated. For each sample, the composite membraneon its coating substrate was placed on a smooth, flat, level marbleslab. A thickness gauge (obtained from Heidenhain Corporation, USA) wasbrought into contact with the composite membrane and the height readingof the gauge was recorded in six different spots arranged in gridpattern on the membrane. Then, the sample was removed from thesubstrate, the gauge was brought into contact with the substrate, andthe height reading was recorded again in the same six spots. The averagethickness of the composite membrane at a given relative humidity (RH) inthe room was calculated as a difference between height readings of thegauge with and without the composite membrane being present on thecoating substrate. The local RH in the room was measured using an RHprobe (obtained from Fluke Corporation). The thickness at 0% RH wascalculated using the following general formula:

${{Thickness}{at}0\%{RH}}=={{( \frac{{{Thickness}{at}{room}{RH}} - \frac{M/A_{{porous}{layer}}}{{Density}_{{porous}{layer}}}}{1 + {\frac{\lambda_{{room}{EH}}}{{EW}_{{ionomer}\_{average}}}*\frac{{Molecular}{weight}_{water}}{{Density}_{water}}*{Density}_{ionomer}}} )**( {1 + {\frac{\lambda_{{RH} = {0\%}}}{{EW}_{{ionomer}_{average}}}*\frac{{Molecular}{weight}_{water}}{{Density}_{water}}*{Density}_{ionomer}}} )} + \frac{M/A_{{porous}{layer}}}{{Density}_{{porous}{layer}}}}==\lbrack{micron}\rbrack$

where density of porous layer represents the skeletal density (2.25g/cm³ for ePTFE), density of ionomer represents density of ionomer at 0%RH (1.96 g/cm³ for PFSA ionomer), density of water is taken to be 0.997g/cm³, molecular weight of water is taken to be 18.015 g/mole, and theparameter λ corresponds to the water uptake of the Ion Exchange Materialin terms of moles of water per mole of acid group at a specified RH. ForPFSA ionomer, the values for λ at any RH in the range from 0 to 100% ingas phase were calculated according the following formula:

λ=80.239×RH⁶−38717×RH⁵−164.451×RH⁴+208.509×RH³−91.052×RH²+21.740×RH¹+0.084

(b) Mass-Per-Area of Composite Membrane

The following test procedure may be used to determine the mass-per-areacomposite membrane prepared in accordance with aspects of the presentdisclosure. A sample of composite material comprising a substrate and acomposite membrane of known area, 10 cm², would be cut from a sheet.After cutting, a sample of composite membrane on its coating substrateis then weighed on a conventional laboratory scale and its weight isrecorded along with the value of RH around the laboratory scale at thetime of measurements. The local RH in the room was measured using an RHprobe (obtained from Fluke Corporation). Then, the sample was removedfrom the substrate, the substrate was weighed using same laboratoryscale and substrate's weight was recorded. The weight of the compositemembrane at a given RH in the room was calculated as a differencebetween weight readings of the scale with and without the compositemembrane being present on the coating substrate.

A composite membrane mass-per-area at 0% RH is then calculated accordingto the following formula:

M/A_(compositemembraneat0%RH) = M/A_(compositemembraneatroomRH%) − Density_(water) * *(ThicknessatroomRH − Thicknessat0%RH) = [g/m²]

(c) Haze for the Composite Membrane

The following haze test procedure was employed on samples of ionexchange membranes having a continuous ionomer phase, which wereprepared in accordance with aspects of the present invention (see, e.g.,FIGS. 3A-3F). Haze test is performed on the composite membranes thatwere dried at ambient conditions (e.g., between 20° C. and 22° C.,relative humidity of 30-70%) for at least 24 hours prior to the test. Asshown in FIGS. 5A and 5B, the haze test procedure includes using a hazemeter or transparency meter 500 to determine the wide-angle scatteringof light by the ion exchange membrane resulting in loss of opticalcontrast with which an object can be seen when viewed through the ionexchange membrane. In the haze meter or transparency meter 500implemented in accordance with aspects of the present invention, asample 505 (e.g., an ion exchange membrane having a continuous ionomerphase) is placed between a light source 510 and a light integrationsphere 515 that is lined with diffusely reflective material and equippedwith a light detector 520, a movable diffusely reflective surface 525,and a trap 530 for low angle scattered and directly transmitted light.

Initially, total transmittance of a sample 505 is measured with the lowangle scattered and direct transmittance light trap 530 being closed bya diffusively-reflecting surface, as shown in FIG. 5A. The closure ofthe low angle scattered and direct transmittance light trap 530 resultsin detection of all light that passed through the sample 505. The totallight transmittance is defined as a ratio of light transmitted by thesample to the incident light on the sample. Thereafter, haze of a sample505 is measured with the low angle scattered and direct transmittancelight trap 530 being opened, as shown in FIG. 5B. Opening of low anglescattered and direct transmittance light trap 530 results in detectionof only the diffuse component of light that passed through the sample505. Haze is defined as a ratio of diffuse transmittance to totaltransmittance of light through a sample.

In some embodiments, the haze of a composite membrane with continuousionomer phase formed via a single pass ionomer coating is between 5% and95%, or 10% and 90%, or 20% and 85%. In alternative embodiments, thehaze of a continuous ionomer phase formed via multiple passes of ionomercoating without a drying step between each pass of coating is between 5%and 95%, or 10% and 90%, or 20% and 85%.

(d) Blistering of the Composite Membrane

The following blister test procedure was employed on samples ofcomposite membrane which were prepared in accordance with aspects of thepresent invention (see, e.g., FIGS. 3A-3D). The blister testingprocedure includes subjecting each sample of composite membrane to astress cycle of immersions for 3 minutes into a beaker containingaqueous sulfuric acid solution of 6 mol/L concentration that was attemperature 80° C. and, subsequently, for 1 minute into a beakercontaining deionized water that was at ambient conditions (e.g., between20° C. and 22° C., relative humidity of 30-70%). The stress cycle wasrepeated consecutively six times. After the stress cycles, each sampleof composite membrane was dried at ambient conditions (e.g., between 20°C. and 22° C., relative humidity of 30-70%), and bubble or blisterdensity was counted. The bubble or blister area may be calculated in anumber of ways including manual observation and measurement and/orautomated techniques such as the use of imaging software. An example ofa publicly available imaging processing software that can be used tocalculate number of and area of blisters is ImageJ developed at NationalInstitute of Health, USA.

FIGS. 6A-6B show a composite membrane 600 prepared in accordance withaspects of the present invention (see, e.g., FIGS. 3A-3D) and aconventional ion exchange membrane 602 at low resolution of 3×3 cm² andhigh resolution of 1×1 before the blister test and high resolution of1×1 cm² after blister test, respectively. As shown in FIG. 6A, both thecomposite membrane 600 and the conventional ion exchange membrane 602exhibit no blisters prior to the blister test performed according to theblister test procedure provided above. As shown in FIG. 6B, thecomposite membrane 600 shows no blisters (i.e. 0 blister/cm²), thus themembrane having 0% blister area, while the conventional ion exchangemembrane 602 shows blisters (i.e. 95 blisters/cm², each blister having aradius of 200 μm and the membrane having 13.5% blister area.

In some embodiments, the bubble or blister area of a composite membranewith continuous ionomer phase formed via a single pass ionomer coatingand after exposure to the blister test procedure is less than 0.3%, lessthan 0.2%, or less than or 0%. In alternative embodiments, the bubble orblister area of a composite membrane with continuous ionomer phaseformed via multiple passes of ionomer coating without a drying stepbetween each pass of coating and after exposure to a blister testprocedure is less than 0.3%, less than 0.2%, or less than 0.1%, or 0%.FIGS. 7A-7C show samples 700, 710, 720 of composite membrane which wereprepared in accordance with aspects of the present invention and have abubble or blister density of less than 0.1%. In some embodiments, thechange in haze of a composite membrane with continuous ionomer phaseformed via a single pass ionomer coating and after exposure to theblister test procedure is 0% or less, between 0% and −60%, or between 0%and −45%, or between 0% and −30%, or between 0% and −21%. In alternativeembodiments, the change in haze of a composite membrane with continuousionomer phase formed via multiple passes of ionomer coating without adrying step between each pass of coating and after exposure to a blistertest is 0% or less, between 0% and −60%, or between 0% and −45%, orbetween 0% and −30%, or between 0% and −21%.

V. Examples

Without intending to limit the scope of the present invention, theapparatus and method of production of the present invention may bebetter understood by referring to the following examples. All samples ofePTFE provided in the following examples were made in accordance withthe teachings of U.S. Pat. No. 3,593,566. Summary of the physicalcharacteristics for porous expanded polytetrafluoroethylene (ePTFE) ispresented in Table 1.

TABLE 1 Physical Characteristics for porous ePTFE used in the examplesMem- Mass/ Non-contact Apparent Bubble brane ID area thickness densityGurley point # g/m2 micron g/cm3 sec kPa 1 30.6 137.1 0.22 26.3 300 2 2657.7 0.46 9.3 127 3 18 26 0.7 12.1 130 4 10.8 30 0.36 9.8 296 5 5.8 12.50.46 6.6 222

1. Comparative Examples—Conventional Multiple Pass Ionomer Manufacturedwith Drying Between Each Step

Example 1.1

A 26.7 micron thick composite membrane comprised of ion exchange polymerperfluoro sulfonic acid resin with EW of 920 g/(mole acid equivalence)reinforced with two layers of expanded porous ePTFE membrane #5 wasprepared using conventional laboratory technique. Initially, awater-ethanol based solution of perfluoro sulfonic acid resin withEW=920 g/mole eq (product FSS2, obtained from Asahi Glass Company) wascoated onto a moving carrier substrate using a slot die, and laminatedwith an ePTFE membrane #5 that was moving in the same direction. Thecarrier substrate is a polymer sheet (obtained from DAICEL VALUE COATINGLTD., Japan) comprising PET and a protective layer of cyclic olefincopolymer (COC), and is oriented with the COC side on top. This laminatewas subsequently dried in an oven at 160° C. and annealed at thattemperature for 1 minute producing a solid coated structure comprisingthe carrier substrate coupled to a polymer layer reinforced withexpanded porous polytetrafluoroethylene.

Thereafter, another amount of water-ethanol based solution of sameperfluoro sulfonic acid resin was applied to the coated structure usinga slot die, and laminated with another ePTFE membrane #5 that was movingin the same direction. The laminate was dried again at 160° C. andannealed at that temperature for 1 minute. Finally, another amount ofwater-ethanol based solution of same perfluoro sulfonic acid resin wasapplied to the coated structure using a slot die, and dried again at160° C. and annealed at that temperature for 1 minute. The resultingcomposite membrane comprised the carrier substrate coupled to a ionexchange polymer layer followed by microporous polytetrafluoroethylenemembrane layer with ion exchange polymer embedded within followed byanother ion exchange polymer layer followed by another microporouspolytetrafluoroethylene membrane layer with ion exchange polymerembedded within followed by another ion exchange polymer layer on topand total thickness of 26.7 micron and mass/area of 54.0 g/m² at 0% RH.The composite membrane was largely transparent with haze value of 5%.

To determine characteristics such as susceptibility of the compositemembrane to blistering in an all-liquid environment with variable ionicstrength, a blister test procedure was performed as described earlier.The haze for the sample of composite membrane 1.5 with discontinuousionomer phase after blister testing as described above increased by 320%to the value of 21.0%. The bubble or blister area for the sample ofcomposite membrane with discontinuous ionomer phase prepared asdescribed above was about 13.5% measured as a ratio of the area of theionomer to the area of the bubbles or blisters in the ionomer. FIG. 6Bshows a photograph of the 3 cm×3 cm and 1 cm×1 cm areal view ofcomposite membrane 602 representing example 1.1 before blister test havebeen conducted and after the blister test been conducted, with themembrane after blister testing having bubbles or blisters 604 in weakinternal interfaces in a layer of ionomer or between the multiplecoatings of the ionomer.

Example 1.2

A 44.2 micron thick composite membrane comprised of ion exchange polymerperfluoro sulfonic acid resin with EW of 810 g/(mole acid equivalence)reinforced with one layer of expanded porous ePTFE membrane #2 wasprepared using conventional laboratory technique. Initially, a ofwater-ethanol based solution of ion exchange perfluoro sulfonic acidresin with EW=810 g/mole eq. (obtained from Shanghai Gore 3FFluoromaterials Co., LTD., China) was coated onto carrier substraterestrained in a frame using a draw down bar, and laminated with an ePTFEmembrane #2. The carrier substrate is a polymer sheet (obtained fromDAICEL VALUE COATING LTD., Japan) comprising PET and a protective layerof cyclic olefin copolymer (COC), and is oriented with the COC side ontop. This laminate was subsequently dried in an oven at 160° C. andannealed at that temperature for 1 minute. Thereafter, another amount ofwater-ethanol based solution of same perfluoro sulfonic acid resin wasapplied to the coated structure using a draw down bar and dried again at160° C. and annealed at that temperature for 1 minute. The resultingcomposite membrane comprised the carrier substrate coupled to a to a ionexchange polymer layer followed by microporous polytetrafluoroethylenemembrane layer with the ion exchange polymer embedded within withanother ion exchange polymer layer on top and had total thickness of44.2 micron and mass/area of 90.5 g/m² at 0% RH. The composite membranewas largely transparent with haze value of 4.6%.

To determine characteristics such as susceptibility of the compositemembrane to blistering in an all-liquid environment with variable ionicstrength, a blister test procedure was performed as described earlierwith the membrane after blister testing having bubbles or blisters inweak internal interfaces in a layer of ionomer or between the multiplecoatings of the ionomer. The haze for the sample of composite membrane1.2 with discontinuous ionomer phase after blister testing as describedabove increased by 35% to the value of 6.3%. The bubble or blister areafor the sample of composite membrane 1.2 with discontinuous ionomerphase prepared as described above was about 1.3% measured as a ratio ofthe area of the ionomer to the area of the bubbles or blisters in theionomer

Example 1.3

A 27.9 micron thick composite membrane comprised of ion exchange polymerperfluoro sulfonic acid resin with EW of 1100 g/(m ole acid equivalence)reinforced with one layer of expanded porous ePTFE membrane #2 wasprepared using conventional laboratory technique. Initially, a ofwater-ethanol based solution of perfluoro sulfonic acid resin withEW=1100 g/mole eq. (D2021, obtained from Ion Power Inc., USA) was coatedonto carrier substrate restrained in a frame using a draw down bar, andlaminated with an ePTFE membrane #2. The carrier substrate is a polymersheet (obtained from DAICEL VALUE COATING LTD., Japan) comprising PETand a protective layer of cyclic olefin copolymer (COC), and is orientedwith the COC side on top. This laminate was subsequently dried in anoven at 160° C. and annealed at that temperature for 1 minute.Thereafter, another amount of water-ethanol based solution of sameperfluoro sulfonic acid resin was applied to the coated structure usinga draw down bar and dried again at 160° C. and annealed at thattemperature for 1 minute. The resulting composite membrane comprised thecarrier substrate coupled to a ion exchange polymer layer followed bymicroporous polytetrafluoroethylene membrane layer with the ion exchangepolymer embedded within with another ion exchange polymer layer on topand had total thickness of 27.9 micron and mass/area of 58.4 g/m² at 0%RH. The composite membrane was largely transparent with haze value of16.8%.

To determine characteristics such as susceptibility of the compositemembrane to blistering in an all-liquid environment with variable ionicstrength, a blister test procedure was performed as described earlierwith the membrane after blister testing having bubbles or blisters inweak internal interfaces in a layer of ionomer or between the multiplecoatings of the ionomer. The haze for the sample of composite membrane1.3 with discontinuous ionomer phase after blister testing as describedabove increased by 34% to the value of 22.6%. The bubble or blister areafor the sample of composite membrane 1.3 with discontinuous ionomerphase prepared as described above was about 0.5% measured as a ratio ofthe area of the ionomer to the area of the bubbles or blisters in theionomer.

Example 1.4

A 22.7 micron thick composite membrane comprised of ion exchange polymerperfluoro sulfonic acid resin with EW of 900 g/(mole acid equivalence)reinforced with one layer of expanded porous ePTFE membrane #3 wasprepared using conventional laboratory technique. Initially, a ofwater-ethanol based solution of perfluoro sulfonic acid resin withEW=900 g/mole eq. (obtained from Shanghai Gore 3F Fluoromaterials Co.,LTD., China) was coated onto carrier substrate restrained in a frameusing a draw down bar, and laminated with an ePTFE membrane #3. Thecarrier substrate is a polymer sheet (obtained from DAICEL VALUE COATINGLTD., Japan) comprising PET and a protective layer of cyclic olefincopolymer (COC), and is oriented with the COC side on top. This laminatewas subsequently dried in an oven at 160° C. and annealed at thattemperature for 1 minute. Thereafter, another amount of water-ethanolbased solution of same perfluoro sulfonic acid resin was applied to thecoated structure using a draw down bar and dried again at 160° C. andannealed at that temperature for 1 minute. The resulting compositemembrane comprised the carrier substrate coupled to a ion exchangepolymer layer followed by microporous polytetrafluoroethylene membranelayer with the ion exchange polymer embedded within with another ionexchange polymer layer on top and had total thickness of 22.7 micron andmass/area of 47.1 g/m² at 0% RH. The composite membrane was largelytransparent with haze value of 19.4%.

To determine characteristics such as susceptibility of the compositemembrane to blistering in an all-liquid environment with variable ionicstrength, a blister test procedure was performed as described earlierwith the membrane after blister testing having bubbles or blisters inweak internal interfaces in a layer of ionomer or between the multiplecoatings of the ionomer. The haze for the sample of composite membrane1.4 with discontinuous ionomer phase after blister testing as describedabove increased by 45% to the value of 28%. The bubble or blister areafor the sample of composite membrane 1.4 with discontinuous ionomerphase prepared as described above was about 0.3% measured as a ratio ofthe area of the ionomer to the area of the bubbles or blisters in theionomer.

Example 1.5

A 17.9 micron thick composite membrane comprised of ion exchange polymerperfluoro sulfonic acid resin with EW of 900 g/(mole acid equivalence)reinforced with one layer of expanded porous ePTFE membrane #4 wasprepared using conventional laboratory technique. Initially, a ofwater-ethanol based solution of perfluoro sulfonic acid resin withEW=900 g/mole eq. (obtained from Shanghai Gore 3F Fluoromaterials Co.,LTD., China) was coated onto carrier substrate restrained in a frameusing a draw down bar, and laminated with an ePTFE membrane #4. Thecarrier substrate is a polymer sheet (obtained from DAICEL VALUE COATINGLTD., Japan) comprising PET and a protective layer of cyclic olefincopolymer (COC), and is oriented with the COC side on top. This laminatewas subsequently dried in an oven at 160° C. and annealed at thattemperature for 1 minute. Thereafter, another amount of water-ethanolbased solution of same perfluoro sulfonic acid resin was applied to thecoated structure using a draw down bar and dried again at 160° C. andannealed at that temperature for 1 minute. The resulting compositemembrane comprised the carrier substrate coupled to a ion exchangepolymer layer followed by microporous polytetrafluoroethylene membranelayer with the ion exchange polymer embedded within with another ionexchange polymer layer on top and had total thickness of 17.9 micron andmass/area of 36.7 g/m² at 0% RH. The composite membrane was largelytransparent with haze value of 5.7%.

To determine characteristics such as susceptibility of the compositemembrane to blistering in an all-liquid environment with variable ionicstrength, a blister test procedure was performed as described earlierwith the membrane after blister testing having bubbles or blisters inweak internal interfaces in a layer of ionomer or between the multiplecoatings of the ionomer. The haze for the sample of composite membrane1.5 with discontinuous ionomer phase after blister testing as describedabove increased by 31% to the value of 7.5%. The bubble or blister areafor the sample of composite membrane 1.5 with discontinuous ionomerphase prepared as described above was about 6.3% measured as a ratio ofthe area of the ionomer to the area of the bubbles or blisters in theionomer.

The data for comparative examples 1.1-1.5 is summarized in Table 2.

TABLE 2 Summary of data for Comparative Examples 1.1-1.5 Compositemembrane Blister Haze, area, Ionomer Thickness Mass/area After After EWat at Haze, blister Haze blister Example Example g/mole ePTFE 0% RH 0%RH Initial test change test # Type eq. # micron g/m² Construction % % %% 1.1 Comparative 920 5 26.7 54.0 Two  5.0% 21.0% 320.0% 13.5%microporous membrane layers with ion exchange polymer embedded withinand three ion exchange polymerlayers 1.2 Comparative 810 2 44.2 90.5 One 4.6%  6.3%  35.1%  1.3% microporous membrane layer with ion exchangepolymer embedded within and two ion exchange polymer layers 1.3Comparative 1100 2 27.9 58.4 One 16.8% 22.6%  34.3%  0.5% microporousmembrane layer with ion exchange polymer embedded within and two ionexchange polymer layers 1.4 Comparative 900 3 22.7 47.1 One 19.4% 28.0% 44.5%  0.3% microporous membrane layer with ion exchange polymerembedded within and two ion exchange polymer layers 1.5 Comparative 9004 17.9 36.7 One  5.7%  7.5%  30.9%  6.3% microporous membrane layer withion exchange polymer embedded within and two ion exchange polymer layers

2. Inventive Examples—A Composite Membrane with Continuous Ionomer PhaseManufactured with Single Pass Ionomer Coating in Accordance with Aspectsof the Present Invention

Example 2.1

A 21.6 micron thick composite membrane comprising of ion exchangepolymer perfluoro sulfonic acid resin with EW of 820 g/(mole acidequivalence) reinforced with expanded porous polytetrafluoroethylenemembrane #3 was prepared using conventional laboratory technique.Initially, a of water-ethanol based solution of perfluoro sulfonic acidresin with EW=820 g/mole eq. (product IW100-800, obtained from AsahiGlass Company) was coated onto a moving carrier substrate using a slotdie, and laminated with an ePTFE membrane #3 that was moving in the samedirection. The carrier substrate is a polymer sheet (obtained fromDAICEL VALUE COATING LTD., Japan) comprising PET and a protective layerof cyclic olefin copolymer (COC), and is oriented with the COC side ontop. This laminate was subsequently dried in an oven at 160° C. andannealed at that temperature for 1 minute producing a solid coatedstructure comprising the carrier substrate coupled to an ion exchangepolymer layer followed by microporous polytetrafluoroethylene membranelayer with the ion exchange polymer embedded within and had totalthickness of 21.6 micron and mass/area of 44.9 g/m² at 0% RH. As can beseen from FIGS. 3E-3F, the resulting composite membrane wascharacterized by having ion exchange material that is embedded withinthe microporous polymer structure leaving a non-occlusive portion of themicroporous polymer structure closest to the first surface and forming alayer on the second surface of the microporous polymer structure Theresulting composite membrane was had haze value of 65%.

To determine characteristics such as susceptibility of the compositemembrane to blistering in an all-liquid environment with variable ionicstrength, a blister test procedure was performed as described earlier.The haze for the sample of composite membrane 1.5 with discontinuousionomer phase after blister testing as described above decreased by−6.2% to the value of 61.0%. The bubble or blister area for sample ofcomposite membrane 2.1 with continuous ionomer phase prepared asdescribed above was about 0% measured as a ratio of the area of theionomer to the area of the bubbles or blisters in the ionomer. FIG. 6Ashows photographs of a 3 cm×3 cm and 1 cm×1 cm areal view of compositemembrane 600 before blister test have been conducted and after theblister test been conducted, with the membrane after blister testinghaving an absence of bubbles or blisters.

Example 2.2

A 44.6 micron thick composite membrane comprised of ion exchange polymerperfluoro sulfonic acid resin with EW of 810 g/(mole acid equivalence)reinforced with one layer of expanded porous ePTFE membrane #1 wasprepared using conventional laboratory technique. Initially, a ofwater-ethanol based solution of perfluoro sulfonic acid resin withEW=810 g/mole eq. (obtained from Shanghai Gore 3F Fluoromaterials Co.,LTD., China) was coated onto carrier substrate restrained in a frameusing a draw down bar, and laminated with an ePTFE membrane #1. Thecarrier substrate is a polymer sheet (obtained from DAICEL VALUE COATINGLTD., Japan) comprising PET and a protective layer of cyclic olefincopolymer (COC), and is oriented with the COC side on top. This laminatewas subsequently dried in an oven at 160° C. and annealed at thattemperature for 1 minute producing a solid coated structure comprisingthe carrier substrate coupled to a polymer layer reinforced withexpanded porous polytetrafluoroethylene. The resulting compositemembrane comprised the carrier substrate coupled to an ion exchangepolymer layer followed by microporous polytetrafluoroethylene membranelayer with the ion exchange polymer embedded within and had totalthickness of 44.6 micron and mass/area of 91.8 g/m² at 0% RH. Theresulting composite membrane was characterized by having ion exchangematerial that is embedded within the microporous polymer structureleaving a non-occlusive portion of the microporous polymer structureclosest to the first surface and forming a layer on the second surfaceof the microporous polymer structure. The composite membrane had hazevalue of 24.4%.

To determine characteristics such as susceptibility of the compositemembrane to blistering in an all-liquid environment with variable ionicstrength, a blister test procedure was performed as described earlierwith the composite membrane after blister testing having an absence ofbubbles or blisters. The haze for the sample of composite membrane 2.2with continuous ionomer phase after blister testing as described abovedecreased by −11.3% to the value of 21.6%. The bubble or blister areafor the sample of composite membrane 2.2 with continuous ionomer phaseprepared as described above was about 0% measured as a ratio of the areaof the ionomer to the area of the bubbles or blisters in the ionomer.

Example 2.3

A 28.1 micron thick composite membrane comprised of ion exchange polymerperfluoro sulfonic acid resin with EW of 1100 g/(m ole acid equivalence)reinforced with one layer of expanded porous ePTFE membrane #1 wasprepared using conventional laboratory technique. Initially, a ofwater-ethanol based solution of perfluoro sulfonic acid resin withEW=1100 g/mole eq. (D2021, obtained from Ion Power Inc., USA) was coatedonto carrier substrate restrained in a frame using a draw down bar, andlaminated with an ePTFE membrane #1. The carrier substrate is a polymersheet (obtained from DAICEL VALUE COATING LTD., Japan) comprising PETand a protective layer of cyclic olefin copolymer (COC), and is orientedwith the COC side on top. This laminate was subsequently dried in anoven at 160° C. and annealed at that temperature for 1 minute. Theresulting composite membrane comprised the carrier substrate coupled toa microporous polytetrafluoroethylene membrane layer with the ionexchange polymer embedded within and had total thickness of 28.1 micronand mass/area of 59.5 g/m² at 0% RH. The resulting composite membranewas characterized by having ion exchange material that is embeddedwithin the microporous polymer structure leaving a non-occlusive portionof the microporous polymer structure closest to the first surface andnot having a layer on the second surface of the microporous polymerstructure. The composite membrane had haze value of 27.8%.

To determine characteristics such as susceptibility of the compositemembrane to blistering in an all-liquid environment with variable ionicstrength, a blister test procedure was performed as described earlierwith the composite membrane after blister testing having an absence ofbubbles or blisters. The haze for the sample of composite membrane 2.3with continuous ionomer phase after blister testing as described abovedecreased by −5.9% to the value of 26.2%. The bubble or blister area forthe sample of composite membrane 2.3 with continuous ionomer phaseprepared as described above was about 0% measured as a ratio of the areaof the ionomer to the area of the bubbles or blisters in the ionomer.

Example 2.4

A 23.2 micron thick composite membrane comprised of ion exchange polymerperfluoro sulfonic acid resin with EW of 900 g/(mole acid equivalence)reinforced with one layer of expanded porous ePTFE membrane #2 wasprepared using conventional laboratory technique. Initially, a ofwater-ethanol based solution of perfluoro sulfonic acid resin withEW=900 g/mole eq. (obtained from Shanghai Gore 3F Fluoromaterials Co.,LTD., China) was coated onto carrier substrate restrained in a frameusing a draw down bar, and laminated with an ePTFE membrane #2. Thecarrier substrate is a polymer sheet (obtained from DAICEL VALUE COATINGLTD., Japan) comprising PET and a protective layer of cyclic olefincopolymer (COC), and is oriented with the COC side on top. This laminatewas subsequently dried in an oven at 160° C. and annealed at thattemperature for 1 minute. The resulting composite membrane comprised thecarrier substrate coupled to a microporous polytetrafluoroethylenemembrane layer with the ion exchange polymer embedded within and hadtotal thickness of 23.2 micron and mass/area of 49.2 g/m² at 0% RH. Theresulting composite membrane was characterized by having ion exchangematerial that is embedded within the microporous polymer structureleaving a non-occlusive portion of the microporous polymer structureclosest to the first surface and not having a layer on the secondsurface of the microporous polymer structure. The composite membrane hadhaze value of 35.2%.

To determine characteristics such as susceptibility of the compositemembrane to blistering in an all-liquid environment with variable ionicstrength, a blister test procedure was performed as described earlierwith the composite membrane after blister testing having an absence ofbubbles or blisters. The haze for the sample of composite membrane 2.4with continuous ionomer phase after blister testing as described abovedecreased by −20.7% to the value of 27.9%. The bubble or blister areafor the sample of composite membrane 2.4 with continuous ionomer phaseprepared as described above was about 0% measured as a ratio of the areaof the ionomer to the area of the bubbles or blisters in the ionomer.

Example 2.5

A 18.4 micron thick composite membrane comprised of ion exchange polymerperfluoro sulfonic acid resin with EW of 900 g/(mole acid equivalence)reinforced with one layer of expanded porous ePTFE membrane #3 wasprepared using conventional laboratory technique. Initially, a ofwater-ethanol based solution of perfluoro sulfonic acid resin withEW=900 g/mole eq. (obtained from Shanghai Gore 3F Fluoromaterials Co.,LTD., China) was coated onto carrier substrate restrained in a frameusing a draw down bar, and laminated with an ePTFE membrane #3. Thecarrier substrate is a polymer sheet (obtained from DAICEL VALUE COATINGLTD., Japan) comprising PET and a protective layer of cyclic olefincopolymer (COC), and is oriented with the COC side on top. This laminatewas subsequently dried in an oven at 160° C. and annealed at thattemperature for 1 minute. The resulting composite membrane comprised thecarrier substrate coupled to a polymer layer reinforced with expandedporous polytetrafluoroethylene and had total thickness of 18.4 micronand mass/area of 38.6 g/m² at 0% RH. The resulting composite membranewas characterized by having ion exchange material that is embeddedwithin the microporous polymer structure leaving a non-occlusive portionof the microporous polymer structure closest to the first surface andhaving a layer on the second surface of the microporous polymerstructure. The composite membrane had haze value of 77.3%.

To determine characteristics such as susceptibility of the compositemembrane to blistering in an all-liquid environment with variable ionicstrength, a blister test procedure was performed as described earlierwith the composite membrane after blister testing having an absence ofbubbles or blisters. The haze for the sample of composite membrane 2.5with continuous ionomer phase after blister testing as described abovedecreased by −8.7% to the value of 60.5%. The bubble or blister area forthe sample of composite membrane 2.5 with continuous ionomer phaseprepared as described above was about 0% measured as a ratio of the areaof the ionomer to the area of the bubbles or blisters in the ionomer.

The data for inventive examples 2.1-2.5 is summarized in Table 3.

TABLE 3 Summary of data for inventive examples 2.1-2.5 Compositemembrane Blister Haze, area, Ionomer Thickness Mass/area After After EWat at blister Haze blister Example Example g/mole ePTFE 0% RH 0% RHHaze, test change test # Type eq. # micron g/m² Construction Initial % %% 2.1 Inventive  820 3 21.6 44.9 One 65.0% 61.0%  −6.2% 0.0% microporousmembrane layerwith ion exchange polymer embedded within and one ionexchange polymer layers 2.2 Inventive  810 1 44.6 91.8 One 24.4% 21.6%−11.3% 0.0% microporous membrane layerwith ion exchange polymer embeddedwithin and one ion exchange polymer layers 2.3 Inventive 1100 1 28.159.5 One 27.8% 26.2%  −5.9% 0.0% microporous membrane layerwith ionexchange polymer embedded within 2.4 Inventive  900 2 23.2 49.2 One35.2% 27.9% −20.7% 0.0% microporous membrane layerwith ion exchangepolymer embedded within 2.5 Inventive  900 3 18.4 38.6 One 77.3% 60.5% −8.7% 0.0% microporous membrane layerwith ion exchange polymer embeddedwithin and one ion exchange polymer layers

While the invention has been described in detail, modifications withinthe spirit and scope of the invention will be readily apparent to theskilled artisan. It should be understood that aspects of the inventionand portions of various embodiments and various features recited aboveand/or in the appended claims may be combined or interchanged either inwhole or in part. In the foregoing descriptions of the variousembodiments, those embodiments which refer to another embodiment may beappropriately combined with other embodiments as will be appreciated bythe skilled artisan. Furthermore, the skilled artisan will appreciatethat the foregoing description is by way of example only, and is notintended to limit the invention.

We claim:
 1. A method of forming the composite membrane, the methodcomprising: (a) providing a support layer, (b) applying an ion exchangematerial to the support layer in one step, (c) obtaining a microporouspolymer structure comprising at least one microporous polymer layer; (d)laminating the at least one microporous polymer layer to the ionexchange material to form an impregnated microporous polymer structurehaving a continuous ionomer phase, (e) applying an ion exchange materialon a top surface of the impregnated microporous polymer structureaccording to method step (d), (f) drying the impregnated microporouspolymer structure to form the composite membrane having a continuousionomer phase, and (g) annealing thermally the composite membrane. 2.The method according to claim 1, wherein no internal interface ispresent between applications of the ion exchange material, themicroporous polymer structure, or any combination thereof.
 3. The methodaccording to claim 1, wherein the drying and annealing thermally of thecomposite membrane is conducted at a temperature from 160 to 220° C. 4.The method according to claim 1, wherein the ion exchange material isapplied in steps (b) and (e) without an intervening drying step.
 5. Themethod according to claim 1, wherein the composite membrane comprises: amicroporous polymer structure; and an ion exchange material at leastpartially embedded within the microporous polymer structure andrendering at least a portion of the microporous polymer structureocclusive, wherein the ion exchange material forms a continuous ionomerphase within the composite membrane, wherein the composite membraneincludes multiple layers of the ion exchange material provided on top ofone another which do not have any internal interface between the layers,and wherein the composite membrane has a haze which is the ratio ofdiffuse transmittance to total transmittance of light through thecomposite membrane and the composite membrane exhibits a change of thehaze of 0% or less after being subjected to a blister test procedure. 6.The method according to claim 5, wherein the composite membranecomprises a bottom surface and an opposing top surface, the compositemembrane further comprising: an additional layer of ion exchangematerial is provided at the bottom surface of the composite membrane. 7.The method according to claim 5, wherein the blister test procedureincludes: at step one, immersing the composite membrane for 3 minutes inan 6 mol/L aqueous sulfuric acid solution at 80° C., at step two,removing the composite membrane from the aqueous sulfuric acid solution,at step three, immersing the composite membrane for 1 minute indeionized water at ambient conditions, at step four, removing thecomposite membrane from the deionized water, repeating cycle composed ofsteps one through four at least two times, at step five, drying thecomposite membrane at ambient conditions, and at step six, countingbubbles or blisters formed on the composite membrane.
 8. The methodaccording to claim 5, wherein a haze value of the composite membraneprior to the blister test procedure is between 5% and 95%.
 9. The methodaccording to claim 5, wherein the bubble or blister area of a compositemembrane with a continuous ionomer phase after exposure to the blistertest procedure is less than 0.3%.
 10. The method according to claim 1,wherein the microporous polymer structure comprises expandedpolytetrafluoroethylene.
 11. The method according to claim 1, whereinthe microporous polymer structure comprises a hydrocarbon polyolefin.12. The method according to claim 11, wherein the hydrocarbon polyolefincomprises polyethylene, polypropylene, or polystyrene.
 13. The methodaccording to claim 1, wherein the ion exchange material comprises atleast one ionomer.
 14. The method according to claim 1, wherein the atleast one ionomer comprises a proton conducting polymer.
 15. The methodaccording to claim 14, wherein the proton conducting polymer comprisesperfluorosulfonic acid.
 16. A flow battery comprising: a cathodereservoir including a positive electrolyte fluid; an anode reservoirincluding a negative electrolyte fluid; and an exchange region includinga composite membrane positioned between first side having a positiveelectrode and second side having a negative electrode, the compositemembrane, comprising: a microporous polymer structure; and an ionexchange material at least partially embedded within the microporouspolymer structure and rendering at least a portion of the microporouspolymer structure occlusive, wherein the ion exchange material forms acontinuous ionomer phase within the composite membrane, wherein thecomposite membrane includes multiple layers of the ion exchange materialprovided on top of one another which do not have any internal interfacebetween the layers, and wherein the composite membrane has a haze whichis the ratio of diffuse transmittance to total transmittance of lightthrough the composite membrane and the composite membrane exhibits achange of the haze of 0% or less after being subjected to a blister testprocedure, wherein the cathode reservoir is connected via a first pumpto the first side of the exchange region, and the anode reservoir isconnected via a second pump to the second side of the exchange region.17. A composite membrane prepared by a process comprising: obtaining anuntreated microporous polymer structure; applying an impregnant solutioncomprising an ion exchange material to the untreated microporous polymerstructure to form a treated microporous polymer structure having acontinuous ionomer phase, wherein the composite membrane includesmultiple layers of the ion exchange material provided on top of oneanother which do not have any internal interface between the layers; anddrying and thermally annealing the treated microporous polymer structureto form the composite membrane, wherein the ion exchange material formsa continuous ionomer phase within the composite membrane, wherein thecomposite membrane has a haze which is the ratio of diffusetransmittance to total transmittance of light through the compositemembrane and the composite membrane exhibits a change of the haze of 0%or less after being subjected to a blister test procedure.